View Full Version : GPS error back?

26-09-2001, 12:45 PM
I checked my GPS in the driveway today and according to my marks - my house had moved 35mt to the SW.
I guess the SA (selective availablity) is back in force as a result of a pending war?

Dave >
PS - Just checked it again and I'm now 10mt to the sth!

26-09-2001, 01:24 PM

You have raised a pertinent point at times of conflict. It pays to always check before leaving home. There is a deliberate error factor in most readings during normal times but, at times such as we are going through now, it is wise not to rely too greatly on the accuracy of our GPS readings.


PS Was enjoying the Boat Show when I saw this hirsute hatted bloke on stage. My missus asked if we should put our umbrella up due to pending rain. I told her you probably sleep in the bloody hat!!!!!

26-09-2001, 03:24 PM
Nugget, I think I've answered this in general somewhere else today and since then I've looked at some data for the 72 hours to 9am yesterday (Monday 24/09/01).

The 95% accuracy for that period was under 10 metres and the current log file to right now shows no changes to this trend.

There has been this expectation by some that SA will be back on but can't really see this being the case. If SA does come back (if at all) it will most likely be regional (a region elsewhere).

One other event that could cause some issues (maybe?) was a very powerful X-class solar flare which erupted Monday morning. That was expected to sweep past earth late Tuesday (today) or early Wednesday causing geomagnetic storms which have been dubbed "the mother of all storms"

Cheers, Kerry.

27-09-2001, 10:12 AM
Thanks for your input Kerry - I'll have to bow to your obviously greater knowledge on the issue than the rest of us.
There must be some other explanaision as I have checked and rechecked over the past 24hrs and I am getting variations of between 38mts and 5 mts from my home coordinates which have previously remained stable for the past 11 months.
The staff at the TMQ stand at the Boat Show also had some concerns over variations in readings - they were the ones that gave me the idea that the SA might be back in force.
Maybe its tropospheric ducting, variations in the ionisphere or pending Amagedon but I am definately getting variation that has not been obvious prior to the past 10 days or so.
- the again mybe the GPS is on the blink?

Thanks again for you input - cheers for now

Dave ><>

29-09-2001, 04:16 AM
Things still just appear to be going round and round with very little change. There will be changes from day to day as sattelites go in and out of the system for maintainence etc but that generally only occurs over the U.S within view of the Master Control Station.

Looking further afield some comparisons from a few locations around the world. The values quoted below are distance RMS based on the mean position of a particular site on that particular day. Data is over 24 hours at 30 second intervals. Regardless of the receiver type the important bit is the difference.

Tidbinbilla (deep space tracking station outside Canberra)
7/9/01 - 2.9m
25/9/01 - 3.2m

Manama (Bahrain - Persian Gulf)
7/9/01 - 5.6m
25/9/01 - 7.5m

Chatham (Barnstable County - Massachusetts USA East coast)
7/9/01 - 5.9m
25/9/01 - 6.8m

Lafayette (Contra County - California USA West coast)
7/9/01 - #5.5m
25/9/01 - 8.7m

Assuming there was no SA back on the 7/9/01 there's also no indication in those figures that anything has changed since (but especially on 25/9/01). Appears business as normal but if you have dates/times of problems then these can be specifically checked out.

But apart from all that the non speculative answer is http://www.igeb.gov/sa.shtml

Cheers, Kerry.